Hydrogen peroxide is inexpensive, non-corrosive and environmentally-friendly because only water is produced as a by-product after reaction, and is an excellent oxidant for use in industry.
As a process for producing an epoxy compound from olefins by using hydrogen peroxide as an epoxidizing agent (oxidant), there have been conventionally known: (1) an epoxidation process by using hydrogen peroxide in the presence of quaternary ammonium chloride, phosphoric acids and a tungsten metal salt (see, Patent Documents 1 and 2 below); (2) an epoxidation process in an organic solvent by using a phase transfer catalyst, such as a quaternary ammonium salt, and using, as catalysts, tungstic acids and α-aminomethylphosphonic acid (see, Patent Document 3 below); (3) an epoxidation process in a toluene solvent in the presence of quaternary ammonium hydrogensulfate, phosphoric acids and a tungsten oxide compound obtained by reacting a tungsten compound with hydrogen peroxide (see, Patent Document 4 below); (4) an epoxidation process by using a multi-component oxidation catalyst containing a tungsten compound, a quaternary ammonium salt, phosphoric acids and/or boric acids, and hydrogen sulfate in the presence of an organic solvent, such as toluene (see, Patent Document 5 below); and (5) an epoxidation process in a chloroform solvent by using a catalyst having both phase transfer ability and epoxidation ability, such as a cetylpyridinium salt of a heteropoly acid (see, Non-Patent Document 1 below). However, these catalyst systems involve use of an organic solvent, and moreover, use of a quaternary ammonium salt, and therefore suffer from the problem that a quaternary ammonium salt-derived impurity is unavoidably mixed in an organic reaction solution to deteriorate the quality. In addition, due to a quaternary ammonium salt-derived decomposition product, an epoxy group causes cationic polymerization during distillation for purification. A reaction system where a reaction proceeds without using an organic solvent has been also reported (see, Patent Document 6 below). However, this system substantially has the same problem, though an organic solvent needs not be used in the reaction.
As a process using a catalyst other than a tungsten compound, there are known: (6) an epoxidation process by using hydrogen peroxide and using a catalyst prepared by loading methyl trioxorhenium (CH3ReO3) and a strong organic base compound on an inorganic oxide support (see, Patent Document 7 below); (7) an epoxidation process by using hydrogen peroxide in the presence of a titanium-containing zeolite catalyst and an additive containing a tertiary amine, a tertiary amine oxide or a mixture thereof (see, Patent Document 8 below); and (8) an epoxidation process by using hydrogen peroxide in the presence of a fluoroalkyl ketone (see, Non-Patent Document 2 below). However, these processes are a process having low catalytic efficiency, requiring an excess of hydrogen peroxide, and being subject to many restrictions, such as applicability only to a small molecule substrate.
A process of reacting hydrogen peroxide and an organic nitrile compound with a carbon-carbon double bond in the presence of a carbonate, hydrogencarbonate or the like of an alkali metal is also known (see, Non-Patent Document 3 and Patent Document 9, below). However, this process has a problem that not only contamination of a slight amount of an alkali metal is unavoidable but also particularly when a compound having an ester bond is employed, the ester bond is liable to be hydrolyzed with the alkali metal salt during epoxidation reaction and purification, leading to reduction in the yield.